The present invention relates to an integrated circuit for measuring the distance which can accurately detect the position with respect to conductive material such as metal. Technology of detecting the position with respect to the conductive material has been applied to various machines in the industrial field. Therefore, an integrated circuit for measuring the distance of the present invention can be widely applied in the whole industrial field. If the integrated circuit for measuring the distance of the present invention is used for measuring the position of a robot arm, highly precise control of the robot arm can be achieved. For this reason, the integrated circuit for measuring the distance of the present invention can be applied to all manufacturing processes performed by using a robot. Further, when the integrated circuit for measuring the distance of the present invention is stored within a position detector, highly precise detection of position can be realized.
In general, an electronic circuit is divided into two circuits, a lump circuit and a distributed circuit. The lump circuit is described by an ordinary differential equation and the distributed circuit is described by a partial differential equation. Therefore, the lump circuit is completely different from the distributed circuit in the mathematical expression. The lump circuit is used for almost all prior art apparatuses for measuring the distance. The distributed circuit is used in the integrated circuit for measuring the distance of the present invention.
In the lump circuit, inductance, capacitance and resistance thereof are constant at all times and their values are not varied even though a frequency is varied. On the other hand, in the distributed circuit, it is possible that capacitance and inductor-thereof are equivalently varied by the skin effect when the frequency is varied. The integrated circuit for measuring the distance of the present invention utilizes the variation of the circuit parameters of the distributed circuit. The present inventor can not find any apparatuses for measuring the distance utilizing the distributed circuit except the integrated circuit for measuring the distance of the present invention.
In an apparatus for measuring the distance, there are two methods, a method of utilizing an optical device and a method of utilizing an electro-magnetic device. A prior art apparatus for measuring the distance, which is the most similar to the present invention, uses a method of detecting the position electro-magnetically. In detecting the position electro-magnetically, there are two methods, a method of using electro-magnetic induction and a method of using electro-statical coupling. These methods comprises the lump circuit. The integrated circuit for measuring the distance of the present invention comprises the distributed circuit. Therefore, the integrated circuit for measuring the distance of the present invention is substantially different from the prior art methods. A prior art apparatus for measuring the distance is described below.
The prior art electro-magnetic apparatus for measuring the distance uses an inductor which is formed by winding wires three-dimensionally. In the ordinary way, the inductor is formed by winding copper wires around magnetic material such as ferrite.
Turning to FIG. 1, an example of an apparatus for measuring the distance using a three-dimensionally distributed inductor is shown. The three-dimensionally distributed inductor is formed by winding coils around magnetic material 21. An alternating current flows into the coils. When the ferrite 22 approaches the three-dimensionally distributed inductor, the current flowing in the coils is varied. The distance between the ferrite 22 and the magnetic material 21 is detected by measuring the variation of the current.
The apparatus for measuring the distance electro-magnetically by using the coils has the following drawbacks.
(1) A comparatively large amount of electric power is required for generating magnetic flux by flowing current in the coils, and therefore a large equipment for electric power source is required. PA1 (2) Calorific value becomes large because of a large amount of current flowing in the coils. PA1 (3) Noises are generated by the magnetic flux leakage. PA1 (4) The cost is high because a process of winding conductive wires is required. PA1 (5) It is impossible to make the apparatus small-sized because of winding the conductive wires three-dimensionally. PA1 (6) Measurement precision can not be improved because the magnetic circuit comprises the magnetic material such as ferrite. PA1 (7) High speed measurement can not be obtained because of the use of low frequency current. PA1 (1) A large amount of electric power is required for a luminous and a light receiving elements. PA1 (2) The luminous and light receiving elements make the structure complicated, and therefore it is difficult to make the apparatus for measuring the distance small-sized. PA1 (3) The cost is high because cheap silicon can not be used for manufacturing the luminous and light receiving elements. PA1 (4) It is difficult to hit the light emitted from the luminous element on the light receiving element perfectly. PA1 (1) A large power supply is required. PA1 (2) When electric power consumption becomes large, calorific value becomes large and temperature becomes high. As a result, the surrounding electronic circuits may not work normally. PA1 (3) Surrounding machines are affected by the noises generated by the strong magnetic flux. PA1 (1) The structure is simple. PA1 (2) The cost is low. PA1 (3) The size is small and the weight is light owing to limited mounting space. PA1 (4) The measurement sensitivity is high. PA1 (5) It is possible to measure at high speed. PA1 (6) It is possible to form an integrated circuit. PA1 (7) The noises generated from the integrated circuit for measuring the distance is small. PA1 (8) The consumption of electric power is small. PA1 (1) The plane inductor of the integrated circuit for measuring the distance of the present invention can be manufactured by using a printing technique. For this reason, the plane inductor can be mass-produced at low cost. On the other hand, in order to manufacture the three-dimensionally distributed inductor, the process of winding conductive wires is required, and therefore the cost becomes high. PA1 (2) The two-dimensionally distributed plane inductor can be small-sized and thinly provided on the surface of the package of the integrated circuit because of its plane form. For this reason, it is possible to make the overall integrated circuit for measuring the distance small-sized. On the other hand, it is difficult to make the three-dimensionally distributed inductor small-sized. PA1 (3) The two-dimensionally distributed plane inductor can utilize the electro-statical coupling efficiently because of its plane structure. Accordingly, the consumption of electric power can be reduced. On the other hand, the three-dimensionally distributed inductor utilizes an electro-magnetic induction instead of the electro-statical coupling because an area capable for utilizing the electro-statical coupling is small. Accordingly, the consumption of electric power becomes large. PA1 (4) In practice, the integrated circuit for measuring the distance of the present invention can be widely applied in the industrial field because the conductive material such as metal is used for various industrial machines. PA1 (5) The electro-statical coupling generated between the plane inductor and the conductive material is close and tight because the plane inductor is distributed two dimensionally. Therefore, the inductance L of the plane inductor varies equivalently, and so can be utilized efficiently. Hence, the measurement sensitivity becomes high. PA1 (6) The integrated circuit for measuring the distance can be widely applied in the manufacturing industry because of the simple structure, light weight and low cost. PA1 (7) It is possible to make the resolving power of measuring the distance high because the plane inductor is located on a plane.
In the integrated circuit for measuring the distance according to the present invention, an alternating current, which changes periodically, flows into a two-dimensionally distributed plane inductor. In general, there are two types in the two-dimensionally distributed plane inductor, a meander type and a spiral type. Turning to FIG. 2, an example of the two-dimensionally distributed plane inductor 1 of the meander type located on the surface of an insulator 3 is shown. The two-dimensionally distributed plane inductor 1 is formed by using conductive material such as copper. The insulator 3 is ordinarily formed by printed-circuit-board material such as paper-phenol and glass-epoxy resin.
Turning to FIG. 3, an example of the two-dimensionally distributed plane inductor 31 of the spiral type located on the surface of the insulator 33 is shown. Current of an extremely high frequency flows in the two-dimensionally distributed plane inductor used for the integrated circuit for measuring the distance of the present invention. In ordinary circumstances, a high frequency of 30 MHz to 1000 MHz is used. When an extremely high frequency is used, the current flows only on the surface of a conductor and does not flow inside of that. This phenomenon is called "skin effect". Since the high frequency is used to measure the distance at high speed, only phenomenon generated around the surface of the plane inductor becomes usable by the skin effect. A comparison between the conductive material approaching the surface of the two-dimensionally distributed plane inductor and that approaching the surface of the three-dimensionally distributed inductor is described below.
In an apparatus for measuring the distance using a method of bringing the conductive material close to all surfaces of the three-dimensionally distributed inductor, the structure thereof becomes extremely complicated. Therefore, in the three-dimensionally distributed inductor, only one out of the six surfaces is usable and inductances of the inductors on the other surfaces can not be varied. However, it can be realized by using a simple structure to bring the conductive material close to the surface of the two-dimensionally distributed plane inductor. When the distance between the conductive material and the plane inductor is reduced, they are electro-statically coupled with each other. It is impossible to efficiently use all of the electro-statical coupling generated on the surfaces of the three-dimensionally distributed inductor, but possible to efficiently use those on the surface of the two-dimensionally distributed plane inductor. The inductance of the inductor is reduced by cancellation of electro-magnetically induced current. A changing rate of the inductance of the three-dimensionally distributed inductor is less than that of the inductance of the two-dimensionally distributed inductor. Hence, higher sensitivity can be obtained by using the two-dimensionally distributed plane inductor than by using the three-dimensionally distributed inductor. As a result, reduction in measuring time can be obtained by flowing high frequency current in the two-dimensionally distributed plane inductor, and a highly precise integrated circuit for measuring the distance can be realized by efficiently utilizing the electro-statical induction generated on the surface of the two-dimensionally distributed inductor.
There is a method of detecting the position optically by using an optical device such as a laser. However, the integrated circuit for measuring the distance of the present invention measures the position electro-magnetically, and so does not use any optical techniques. An apparatus for measuring the distance with the optical device has the following drawbacks.
In an apparatus for measuring the distance using the three-dimensionally distributed inductor, the magnetic flux generated by current flowing in the inductor is used. When the conductive material approaches the three-dimensionally distributed inductor, the generated magnetic flux passes through the conductive material and eddy current flows in the conductive material by means of an electro-magnetic induction phenomenon. By this phenomenon, the three-dimensionally distributed inductor is electro-magnetically coupled to the conductive material. The strength of electro-magnetic coupling between the three-dimensionally distributed inductor and the conductive material is in inverse proportion to the distance between the same. The strength of the generated electro-magnetic coupling is measured by detecting the current flowing in the inductor. Therefore, the distance between the three-dimensionally distributed inductor and the conductive material can be measured by results of measuring the current flowing in the inductor. Hence, it is the generated magnetic flux that the three-dimensionally distributed inductor can use as an integrated circuit for measuring the distance. Consequently, when using the three-dimensionally distributed inductor, only one surface of the three-dimensionally distributed inductor, which the generated magnetic flux goes toward, can be used as an apparatus for measuring the distance, and the other surfaces cannot be used. Therefore, large current is required for generating the strong magnetic flux in raising the sensitivity of the apparatus for measuring the distance. However, if the large current flows in the inductor, the consumption of electric power becomes large. When the consumption of electric power becomes large, the apparatus for measuring the distance has the following drawbacks.
According to the above-mentioned consideration, reducing the current flowing in the inductor and raising the sensitivity are required for manufacturing a highly precise apparatus for measuring the distance. For this reason, the electro-statical coupling, which requires a small amount of current, is more preferable than the electro-magnetic coupling which requires a large amount of current in respect of efficiency. Namely, the inductor for measuring the distance is electro-statically coupled to the conductive material. The inductor for measuring the distance has a two-dimensional structure so as to efficiently utilize the electro-statical coupling. When bringing the conductive material close to the two-dimensionally distributed plane inductor, the electro-statical coupling becomes the maximum, the sensitivity of the plane inductor for measuring the distance is increased, and then the consumption of electric power becomes the minimum. When the two-dimensionally distributed plane inductor is electro-statically coupled to the conductive material, a conductive part of the two-dimensionally distributed plane inductor and the conductive material become capacitors equivalently. Namely, the conductive part of the two-dimensionally distributed plane inductor becomes one electrode of the distributed capacitor and the conductive material becomes the other electrode of that. In general, when the frequency of current flowing in a circuit is increased, the current flowing in the capacitor is increased and the current flowing in the plane inductor is decreased. When the distance between the two-dimensionally distributed plane inductor and the conductive material is short, the inductance of the two-dimensionally distributed inductor is equivalently decreased because of the increased capacity of the distributed capacitor. Namely, the frequency of an oscillator is increased because of the decreased induction. Consequently, the variation of the distance between the two-dimensionally distributed plane inductor and the conductive material can be measured by detecting the frequency variation.
The apparatus for measuring the distance is mostly housed internally in a robot and a machine when being used. The requirements, which the apparatus for measuring the distance must satisfy, are described below.
An object of the present invention is to provide the apparatus for measuring the distance satisfying the above-mentioned requirements.
The above and further object and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.